networks – Proxmox: Add a second redundant / backup gateway

I'm running a physical device with two containers, each running a live service. I am moving this server to a different location within the data center and I want to reduce the downtime. The device will leave a data center provided / 29 and a new company / 24.

I am analyzing how to add a second gateway, a "backup" gateway, not to immediately replace the existing default gateway, but to complement it when the network changes.

The existing configuration looks like this.
A ProxMox table that contains a remote vmbr network and a local vmbr network

Ideally, you could simply add a vmbr2 with the new / 24 and the new gateway and leave it idle until those network conditions exist. Unfortunately, the way networks work seems to prohibit that configuration.

I tried to add a new vmbr in only enp3s0, with the idea of ‚Äč‚Äčtelling remote hands to use that port, but Proxmox does not allow it either because there can only be one gateway in the whole table.

Is there a way to achieve a redundant gateway / backup / if-it-it in complement of a default gateway?